1. Field
The present invention relates to a liquid crystal display device, and more particularly to a backlight of a liquid crystal display device that is adaptive for preventing picture quality deterioration.
2. Description of the Related Art
Generally, a liquid crystal display LCD controls the light transmissivity of liquid crystal cells in accordance with a video signal to display a picture corresponding to the video signal on a liquid crystal display panel where the liquid crystal cells are arranged in a matrix shape.
For this, the liquid crystal display device includes a liquid crystal display panel where liquid crystal cells are arranged in an active matrix shape; and a backlight unit in the rear surface or the side surface of the liquid crystal display panel to illuminate light onto the liquid crystal display panel.
The backlight is divided into an edge type and a direct lighting type in the way of arranging cylindrical fluorescent lamps.
Firstly, in the edge light type, the fluorescent lamps are installed at the outer area to disperse light to the whole surface by use of a light guide panel. The brightness of the edge light type is low because the fluorescent lamp is installed at the side surface and light passes through the light guide panel. Further, complicated optical design technology and process technology on the light guide panel is required for uniform distribution of light.
The direct light type is comparatively brighter and more uniform than the edge light type because multiple fluorescent lamps are arranged on a plane.
In the direct light type, the fluorescent lamp as a light source is mainly a cold cathode fluorescent lamp CCFL that has electrodes inside both the ends thereof. Recently, however, an external electrode fluorescent lamp (EEFL) has been developed. The EEFL has electrodes at the surface of both ends thereof.
The EEFL has no direct collision between electrodes and ions, thus heat generation in the electrode is restrained. In the EEFL, the generation of plasma joule heat is low because the EEFL is driven at high voltage and low current. In addition, self-discharge exists in the EEFL, thus it can be driven with high brightness and high efficiency.
FIGS. 1 and 2 are a perspective view and a plan view representing a prior art backlight unit of a liquid crystal display device using an external electrode fluorescent lamp.
A backlight using an external electrode fluorescent lamp shown in FIGS. 1 and 2 includes a supporter having a first supporter 50 and a second supporter 52 where a lower contact terminal 56 holds both electrode parts 42a, 42b of the external electrode fluorescent lamp 40. Herein, the supporter having the first supporter 50 and the second supporter 52 has a rectangular stick shape and is separated from each other with a designated distance therebetween. The supporter having the first supporter 50 and the second supporter 52 is formed of thermal plastic elastomer TPE and polybutylene terephthalates PBT.
A lower conductive board 54, where a conductive nickel is coated over the original surface of phosphor bronze, beryllium copper, etc., is fixed by a screw 58 and the lower conductive board 54 is cut and bent to form a lower contact terminal 56 in the upper surface of the first supporter 50 and the second supporter 52, wherein the lower contact terminal 56 can hold, and at the same time cover the electrode parts 42a, 42b of the fluorescent lamp 40.
Herein, the first supporter 50, the second supporter 52 and the lower conductive board 54 can be bonded together by glue, heat melt-adhesion, insert injection, etc.
And, there is a cover having a first cover 60 and a second cover 62 that covers the upper part of both the electrode parts 42a, 42b of the external electrode fluorescent lamp 40 with the upper contact terminal 66 on the supporter inclusive of the first supporter 50 and the second supporter 52.
Herein, the first cover 60 and the second cover 62 have a rectangular stick shape and are separated from each other with a designated distance therebetween to correspond to the first supporter 50 and the second supporter 52, respectively.
The first cover 60 and the second cover 62 are made of thermal plastic elastomer TPE and polybutylene terephthalates PBT.
And, an upper conductive board 64, where a conductive nickel is coated over the original surface of phosphor bronze, beryllium copper, etc., is fixed by a screw 68 and the upper conductive board 64 is cut and bent to form an upper contact terminal 66 in the lower surface of the first cover 60 and the second cover 62, wherein the upper contact terminal 66 can hold, and at the same time cover the electrode parts 42a, 42b of the fluorescent lamp 40 that is located at the lower contact terminal 56 of the supporter.
Herein, the first cover 60, the second cover 62 and the upper conductive panel 64 can be bonded together by glue, heat melt-adhesion, insert injection, etc.
Accordingly, an operator holds the external electrode fluorescent lamp 40 to locate the electrode parts 42a, 42b of the external electrode fluorescent lamp 40 at the lower contact terminal 56 which is formed on the supporter having the first supporter 50 and the second supporter 52 that are separated from each other with a designated distance therebetween.
And then, the operator locates the cover having the first cover 60 and the second cover 62 on the supporter having the first supporter 50 and the second supporter 52 that hold the electrode parts 42a, 42b of the external electrode fluorescent lamp 40, at the lower contact terminal 56.
After then, the upper contact terminal 66 of the cover having the first cover 60 and the second cover 62 wraps to hold the upper part of the electrode parts 42a, 42b of the fluorescent lamp and covers the electrode parts 42a, 42b of the external electrode fluorescent lamp 40 that are held by the lower contact terminal 56.
In the prior art backlight unit using the external electrode fluorescent lamp 40, the upper and lower conductive boards 54, 64 are deformed by the heat conducted to the external electrode fluorescent lamp 40. This generates defects in the backlight.
More specifically, if an AC power is supplied to the external electrode fluorescent lamp 40 through the upper and lower contact terminal 54, 64, the external electrode fluorescent lamp 40 is driven. If the external electrode fluorescent lamp 40 is driven in this way, the heat conducted from the external electrode fluorescent lamp 40 causes the upper and lower conductive boards 54, 64, where the conductive nickel is coated on the original surface of the phosphor bronze, beryllium copper, etc., to be extended by thermal expansion. Herein, the extended upper and lower conductive boards 54, 64, as shown in FIG. 3, are separated from the supporter 50, 52 or the cover 60, 62, or expanded in a parallel direction to the supporter 50, 52 or the cover 60, 62, thereby causing the location of the lamp 40 to be changed. This causes the picture quality of the liquid crystal display panel to deteriorate due to the non-uniform light. Thus, the distance between the lamps 40 becomes non-uniform or the extended upper and lower conductive boards 54, 64 are separated from the supporter 50, 52 and the cover 60, 62.